From mboxrd@z Thu Jan  1 00:00:00 1970
From: qiuxishi@huawei.com (Xishi Qiu)
Date: Thu, 14 Jan 2016 20:35:45 +0800
Subject: Have any influence on set_memory_** about below patch ??
In-Reply-To: <20160113111806.GC23370@leverpostej>
References: <5693A740.7070408@huawei.com> <20160111133145.GM6499@leverpostej>
 <569454F6.1060207@huawei.com> <20160112111531.GA4858@leverpostej>
 <5696272E.8090408@huawei.com> <20160113111806.GC23370@leverpostej>
Message-ID: <56979621.1060102@huawei.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 2016/1/13 19:18, Mark Rutland wrote:

> On Wed, Jan 13, 2016 at 06:30:06PM +0800, Xishi Qiu wrote:
>> Hi Mark,
>>
>> If I create swapper page tables by 4kb, not large page, then I use
>> set_memory_ro() to change the pate table flag, does it have the problem
>> too?
> 
> The splitting/merging problem would not apply.
> 
> However, you're going to waste a reasonable amount of memory by not
> using section mappings in the swapper, and we gain additional complexity
> in the page table setup code (which is shared with others things that
> want section mappings).
> 
> What are you exactly actually trying to achieve?
> 

If module allocates some pages and save data on them, and the data will
not be changed during the module running. So we want to use set_memory_ro()
to increase the security. If the data is changed, we can catch someone.

> What memory do you want to mark RO, and why?
> 

The key data, and it will not be changed during the running time.

>>>From a previous discussion [1], we figured out alternative approaches
> for common cases. Do none of those work for your case?
> 

I have not read the patchset carefully, could you tell me the general meaning
of the approaches?

Thanks,
Xishi Qiu

> Thanks,
> Mark.
> 
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-January/397320.html
> 
> .
>